The present invention relates to a flanged member intended to be included as a component in a pressure equipment device, as well as a joint comprising two joint halves in the form of two flanged members and included in a pressure equipment device.
It has been known for a long time to join different parts and components in pressure equipment devices, preferably pipe systems, by using flanged members. By flanged member, also called flange member or only flange, is here intended not just a pipe member, one end of which has been provided with a ring-shaped collar or flange, but also different components which may be included in a pipe system and that have at least one flanged end. It may, for instance, pertain to valves, Y-pieces or joint parts which may have one or more flanged ends for connection to other parts in the pipe system, vessels having a flange for the mounting of a lid, halves of casings for axial flow turbines or the like. The expression “flanged member” in this connection, also be regarded to comprise so-called blind flanges, i.e. an member that is used in order to close a pipe, by the fact that it is mounted on another flanged member in the pipe system or the like. A blind flange is frequently formed as a plate (without opening) that on one hand covers the pipe opening and on the other hand forms the flange, possibly with some type of an axially protruding portion.
So-called flanged joints comprise two flanged members that are closely joined, usually by means of bolts that are screwed through the opposite flange of the two flanged members and with prestress against nuts. Also other types of joining devices may be used, e.g. clips or clamps.
Flanged joints may generally be provided with sealing members or lack sealing members. Sealing members that transfer forces from a flange to another flange are usually denominated gaskets. Sealing members that do not transfer any significant forces from a flange to another and which enable metal-to-metal contact between the flanges are usually denominated seals. The present invention relates in particular to flanged joints without a gasket and which enable metal-to-metal contact, with or without a seal.
Flanged joints and other joints where flanged members are included are used in numerous applications, and the dimensions of the pipes and members that are included may vary substantially. As examples of applications, may be mentioned within the offshore industry, sub sea industry, process industry, petrochemical industry, in power plants, in oil and gas transport pipes, on tankers, etc. The flanged joints and flanged members that are constructed according to conventional technique, with gaskets, and that are used here, are very heavy, space-demanding and expensive. It is given that reliability of the flanged joints as for function and in particular leak tightness has to be guaranteed, since breakdown may cause loss of human life as well as extensive environmental damage and production loss. However, there is in principle always a certain leakage in dismountable flanged joints designed according to conventional technique, and in those cases when fixed welded joints are used instead, a more difficult maintenance and exchange is obtained in return.
Thus, insufficient leak tightness and leakage is among the largest problems as for flanged joints. There may be many reasons for this. A general problem for all types of flanged members and flanged joints is the stresses and loads that arise in the material at the assembly of the flanged ends on the members. In many cases, these also lead to a deformation of the flange, which in turn risks causing deteriorated tightness and problems with leakage. At flanged members where a non-flanged end is welded onto a pipe, which is commonly occurring, frequently these deformations arise as a consequence of the generation of heat during the welding. A known way to try to decrease these problems with stresses in the material is to form the transition between the flange on the flanged end of the member and the non-flanged end as a substantially elliptical area. This known technique is disclosed, for instance, in U.S. Pat. No. 4,183,562 and in WO-A-93/17268.
It is general for all types of flanged joints that in many cases the fact is that the leakage does not arise until after a period of time. This may be due to, e.g., alternating loads and high stresses in combination with thermal loads and vibrations. In many flanged joints, there is also a dynamic condition, which entails that the sealing surfaces become worn and that bolts loose their prestress or cracks as a result of fatigue. Corrosion may also contribute to leakage arising.
A way of trying to cope with these problems of leakage is to form the end surfaces directed towards each other, of two flanged members, so that they are inclined, thereby, in radial cross-section, forming an angle to each other, when they have been brought together but before assembly, so that the distance between the two end surfaces increases in radial direction outwards. Such a solution is also known by said document WO-A-93/17268. However, this leads to an uneven deformation of the end surfaces, which does not provide a good seal. In said document, it is also disclosed how the end surfaces may have part surfaces that are “conical”, something which also results in an uneven deformation and poor seal.
It has also turned out that a flanged joint, having end surfaces that abut sealingly against each other after tightening of the bolts or the like of the joint, still starts to leak due to the fact that it is deformed when the system in which it is included is pressurised by the fact that a fluid begins to flow through the system. Said deformation depends foremost on the pressure in the pipe system, the properties of the material in the flange as well as the dimensions thereof.
The deformation that arises in the end surfaces, for various reasons, some of which have been mentioned above, most often means that they do not preserve their flatness, but even become slightly convex, i.e. bulge outwards. In the simplest case, they become slightly convex already in connection with the bolts being tightened and then foremost around the boltholes, when it is a bolted joint. This results in the innermost contact point between the end surfaces being displaced somewhat outwards in the radial direction, so that no sealing abutment is obtained between the end surfaces farthest in towards the opening of the flanged member. It is the understanding about this problem that is the basis of the present invention.
Moreover, it is also a fact that it is very difficult on the whole to manufacture flanged members having a satisfying flatness on the end surfaces.
An additional reason for insufficient leak tightness, above all after a period of time, is that sealing members, in particular gaskets, age and lose their function.
In this connection, it should be emphasised that the reliability of flanged joints in respect of leak tightness is of primary importance. Also a deteriorated leak tightness that results in a very small leakage may, for instance, constitute a serious hazard when it is environment-negative, unhealthy or flammable materials that are transported in the pipe system.